Applicant is aware of the following pertinent U.S. Pat. Nos
U.S. Pat. No. 3,747,812-Karman et al. (hereinafter referred to as Citation A) PA0 U.S. Pat. No. 3,478,937-Solowey (hereinafter referred to as Citation B) PA0 U.S. Pat. No. 4,267,846-Kontos (hereinafter referred to as Citation C) PA0 U.S. Pat. No. 4,386,606-Tretinyak et al. (hereinafter referred to as Citation D) PA0 U.S. Pat. No. 2,959,170-Laub (hereinafter referred to as Citation E).
The above Citation A discloses a syringe mainly comprising a plunger, a barrel (body) and a pair of clips. Inside of this syringe, a vacuum can be produced before use by pulling out the plunger relative to the barrel and then rotating the plunger to move two brackets provided on the clips into two notches provided in the shaft of the plunger so as to engage the plunger with the clips and thereby retain the produced vacuum. However, as compared with a conventional syringe which mainly comprises only a plunger and a barrel, the construction, assembly and operation of this syringe is more complicated. Consequently, this syringe cannot be manufactured by the same process as that used to produce a conventional syringe and therefore the cost involved in manufacturing this syringe become higher.
That which is disclosed in the above Citation B is a single unit-dose syringe which is used to administer medication into the body cavity, rather than a suction syringe. The plunger as per this Citation is not outwardly returnable after being once depressed. With this syringe, it is impossible to produce and retain a vacuum in the syringe before use. In addition, the locking means shown in FIGS. 4 and 5 of this Citation is made of a pair of pawls, a coil spring, two pins, a spring receiving opening etc., and the construction thereof is quite complicated.
In the above Citation C, a controlled volume blood sampling syringe is disclosed. According to this Citation, the distance which the plunger can move in both inward and outward directions can be controlled. However, with this syringe, it is impossible to produce and retain a vacuum in the barrel before use.
The above Citation D discloses a syringe comprising a plunger, a barrel and a separate locking means for locking the plunger to the barrel. The locking means includes cam means, a handle, and connector means connecting the cam means and the handle. When the locking means is in its locked position, the plunger is forced to one side of the barrel and is pinched or bound between the barrel on one side and cam on the other side, thus locking the plunger against axial movement with respect to the barrel. However, since the locking function is achieved through the deformation of the webs of the plunger and the friction between the cam means and the webs, instead of through more reliable engagement, say, engagement between two step-shaped portions, it is difficult to lock the plunger in an accurate position. Besides, eccentricity of the plunger shank within the barrel might result in the tilt of the piston and destroy the sealing effect of the piston. Furthermore, in addition to that which comprises the aforesaid conventional syringe, the syringe disclosed in Citation D includes a locking means and, therefore, is more expensive to manufacture.
In the above Citation E, a hypodermic syringe, rather than a suction syringe, is disclosed. According to this Citation, before use, the plunger of the syringe is locked in a fixed position by engaging each flange of the barrel, respectively, in a groove formed between a key extending laterally from the proximal end of the plunger and a finger integrally formed with the key. This syringe is intended to be pre-filled with a desired medicament for subsequent use as inoculation against epidemics, rather than to produce and retain a vacuum therein prior to use so as to facilitate a subsequent operation of blood withdrawl.
Although various means, as described above, have been known in the art of syringes for controlling plunger movement relative to the barrel, the art has been deficient in providing a suitable suction syringe which can simultaneously meet all the following requirements such as simple construction, easy operation, low manufacturing cost and accurate locking position of the plunger relative to the barrel.
Therefore, it is toward the solution of this deficiency that the present invention is directed.